. 


61 

G77i 


UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


Intorattg  of  dK 


STUDIES  IN  THE  BIOLOGICAL  SCIENCES 


THE  IMPORTANCE  OF  SEED   CHARACTERISTICS  IN 

THE  NATURAL  REPRODUCTION  OF 

CONIFEROUS  FORESTS 


BY 


JULIUS  VALENTINE  HOFMANN,  M.F.,  Ph.D. 
Special  Lecturer  on  Sylviculture  in  the  University  of  Minnesota 


MINNEAPOLIS 

Bulletin  of  the  University  of  Minnesota 
June    1918 

PRICE:  25  CENTS 


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•Ktttoratig  of  IHt 

STUDIES  IN  THE  BIOLOGICAL  SCIENCES  NUMBER  2 


THE  IMPORTANCE  OF  SEED  CHARACTERISTICS  IN 

THE  NATURAL  REPRODUCTION  OF 

CONIFEROUS  FORESTS 

BY 

JULIUS  VALENTINE  HOFMANN,  M.F.,  Ph.D. 
Special  Lecturer  on  Sylviculture  in  the  University  of  Minnesota 


MINNEAPOLIS 

Bulletin  of  the  University  of  Minnesota 
June   1918 


COPYRIGHT  1918 

BY  THE 
UNIVERSITY  OF  MINNESOTA 


PREFACE 

Acknowledgment  is  made  to  Dr.  F.  E.  Clements  for  assistance  in 
planning  the  laboratory  work  and  to  Professor  J.  P.  Wentling,  under 
whom  the  sylvicultural  work  was  done,  for  many  suggestions  in  the 
development  of  the  study  and  in  the  interpretation  of  the  data.  The 
author  is  indebted  to  the  United  States  Forest  Service  for  the  investi- 
gations he  conducted  while  at  the  Priest  River  and  Wind  River  Experi- 
ment Stations,  especially  to  Mr.  D.  R.  Brewster  for  his  help  at  the  Priest 
River  Experiment  Station.  All  plates  are  original  except  Plates  I  and  II, 
for  which  credit  is  given  the  United  States  Forest  Service. 

JULIUS  V.  HOFMANN 
March  1,  1914 


398316 


CONTENTS 

Page 

Preface iii 

Introduction 1 

Amount  of  seed 1 

Distribution  of  seed 2 

Methods  of  study 3 

Germination  of  seed 6 

Size  of  seed 7 

Viability  of  seed 18 

Seeds  treated  with  chemicals 18 

Summary  and  conclusions 24 

LIST  OF  PLATES 

I.     Migration  chart 4 

II.     View  of  Yacolt  burn 8 

Ill-XL     Seedlings 14 

XII.     View  of  Oregon  National  Forest 20 


THE  IMPORTANCE  OF  SEED  CHARACTERISTICS  IN 

THE  NATURAL  REPRODUCTION  OF 

CONIFEROUS  FORESTS 

INTRODUCTION 

Almost  all  coniferous  trees  are  dependent  on  seed  for  their  perpetuation 
and  distribution.  Although  in  their  natural  state  coniferous  forests  have 
maintained  themselves  and  extended  their  boundaries  with  only  minor  or 
local  changes  of  composition,  this  apparent  equilibrium  in  nature  is  easily 
upset  by  man's  exploitations,  such  as  destructive  lumbering,  repeated 
fires,  and  unregulated  grazing.  The  effort  to  find  the  cause  for  the  ease 
with  which  this  climax  type  of  the  plant  kingdom  is  disturbed  or  entirely 
replaced  led  to  a  study  of  the  seed. 

This  study  has  brought  out  many  valuable  facts  about  seed  character- 
istics and  their  importance  in  the  perpetuation  and  distribution  of  the 
forest.  Seeds  and  their  behavior  have  been  studied  in  the  laboratory  and 
in  the  field  with  special  emphasis  on  the  importance  of  size,  vitality,  length 
of  time  required  to  germinate,  and  other  characteristics. 

AMOUNT  OF  SEED 

The  production  of  seed  is  an  important  factor  in  the  perpetuation  of 
the  tree  species,  although  the  periodicity  of  seed  years  and  quantity  of 
seed  produced  by  one  species  may  vary  widely  from  these  same  factors  in 
another  species.  The  variations  of  seed  production  of  one  species  are 
often  weighed  against  the  same  factors  of  another  species,  to  advantage 
or  disadvantage  as  the  case  may  be.  This  appears  to  be  true  when  associ- 
ated species  such  as  yellow  pine  (Pinus  ponderosd)  and  lodgepole  pine 
(Pinus  contorta)  or  Douglas  fir  (Pseudotsuga  taxi/olio),  hemlock  (Tsuga 
heterophylla),  western  red  cedar  (Thuya  plicata),  and  western  white  pine 
(Pinus  monticold)  are  considered.  The  yellow  pine  is  able  to  compete 
successfully  with  lodgepole  pine  under  conditions  favorable  to  the  yellow 
pine.  The  lodgepole  pine  is,  however,  a  much  more  prolific  seeder,  pro- 
ducing greater  quantities  of  seed  than  does  the  yellow  pine.  What  the 
lodgepole  pine  loses  in  ability  to  contend  with  unfavorable  conditions,  it 
gains  in  having  many  more  seeds  and  consequently  more  seedlings  with 
which  to  begin  the  struggle. 

This  is  also  true  of  the  hemlock  and  its  associates.    If  the  enormot 
quantity  of  seed  produced  annually  by  the  hemlock  had  the  same  chances 
of  success  as  the  species  with  which  it  associates,  such  as  the  Douglas  fir, 
western  white  pine,  and  larch  (Larix  occidentalism  the  entire  forest  would 


2  JULIUS  VALENTINE  HOP  MANN 

soon  be  of  hemlock.  The  small  seed  of  the  cedar  is  a  good  example. 
Although  there  is  much  seed  of  this  species  produced  annually,  the  fact 
that  it  is  small,  produces  a  small  seedling,  and  requires  exceptionally 
favorable  conditions  for  germination  and  establishment,  limits  the  species 
and  prevents  it  from  getting  entire  possession  of  the  ground. 

In  the  Lake  states,  the  jack  pine  (Pinus  divaricatd)  produces  many 
more  seeds  than  the  white  pine  (Pinus  strobus]  or  the  Norway  pine  (Pinus 
resinosa),  and  these  species  are  always  in  keen  competition  with  one 
another,  resulting  in  the  triumph  of  the  jack  pine  in  localities  favorable  to  it. 

Periodicity  of  the  seed  years  is  variable;  so  much  so  that  it  can  not  be 
considered  in  any  practical  application  in  planning  for  future  forest  work. 
It  must,  however,  be  considered  in  determining  when  the  latest  heavy 
crop  of  seed  was  produced.  The  forests  produce  seed  sometimes 
annually  and  sometimes  at  periods  of  two  or  three  years  or  even  more. 
It  is  sufficient  to  know  for  the  purposes  of  management,  whether  the  latest 
crop  was  a  sparse,  medium,  or  heavy  one. 

In  any  average  seed  year,  a  forest  furnishes  enough  seed  to  produce, 
under  favorable  conditions,  an  adequate  stand  of  seedlings.1  The  heavy 
toll  of  rodents,  fungi,  drought,  frost,  and  other  unfavorable  germination 
conditions,  however,  reduces  the  number  of  seedlings  resulting  from  a 
single  crop  to  a  minimum. 

In  regard  to  seed  production  Darwin  says:  "Large  numbers  of  seed 
are  destroyed.  The  greater  the  chance  against  any  given  seed  reaching 
a  suitable  locality  and  attaining  maturity,  the  larger  the  number  of  seeds 
must  the  plant  produce  in  order  to  maintain  its  numbers  and  as  a  general 
rule  the  smaller  will  the  individual  seeds  be.  On  the  contrary  the  greater 
the  chance  that  each  seed  enjoys  of  arriving  at  maturity,  the  smaller  the 
number  of  seeds  that  is  necessary,  and  in  such  cases  it  is  an  advantage 
that  the  seeds  should  be  large." 

DISTRIBUTION  OF  SEED 

Many  species  of  coniferous  trees  bear  seed  with  wings  attached,  being 
thus  adapted  for  wind  distribution.  Most  of  the  seeds  have  a  wing 
attached  to  one  side  of  the  seed  only.  In  an  ordinary  wind  of  ten  or  twelve 
miles  an  hour,  such  seed  when  released  from  the  cone  begins  a  downward 
spiral  course  and  lands  within  150  feet  of  the  base  of  the  tree.  Since  in 
a  large  part  of  our  coniferous  forests  there  is  usually  little  wind  in  the 
p.utumn,  or  seeding  time,  wind  can  be  considered  a  factor  in  seed  distribu- 
tion for  only  short  distances  from  the  seed  trees.  To  be  sure,  the  occasional 
blast  of  wind  at  the  higher  altitudes,  blowing  at  the  rate  of  seventy-five 
miles  an  hour,  as  has  been  measured  by  the  writer  in  the  Cascade 

°f  WCStern  white  pine"     United  Stales  Department  of  Agriculture, 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  3 

Mountains  of  Washington,  may  carry  an  occasional  seed  for  a  long  distance, 
but  satisfactory  reproduction  over  large  areas  never  results  from  a  few 
seeds  sown  in  this  way. 

Animals  play  a  rather  incidental  part  in  seed  distribution,  and  the 
carrying  of  seed  by  birds  may  account  for  the  occasional  trees  found  in 
unusual  places.  The  most  striking  instance  of  animal  distribution  is  seen 
in  the  yellow  pine  regions  where  squirrels,  chipmunks,  and  mice  collect 
and  cache  seeds  and  cones.  Usually  the  caches  are  under  logs,  in 
stumps,  or  other  hiding  places.  Often  on  the  grassy  slopes  of  the  yellow 
pine  region  squirrels  store  separate  cones  under  tufts  of  grass.  The  writer 
has  examined  and  collected  cones  from  such  caches  that  covered  areas 
200  square  feet  or  more.  Mice  also  cache  small  piles  of  clean  seed  under 
grass  tufts.  Naturally  rodents  do  not  find  all  of  the  stored  cones  and 
seed,  and  in  this  way  they  become  planters  of  seed  even  though  they  take 
heavy  toll  for  their  work.  This  accounts  for  the  patches  of  yellow  pine 
reproduction  on  some  of  the  grassy  slopes  of  western  Montana  and  Idaho. 
Tufts  of  yellow  pine  have  been  found  containing  from  ten  to  twenty 
seedlings. 

METHODS    OF    STUDY 

To  determine  seed  distribution,  belt  transects  8}^  feet  wide  were  run 
2>£  chains  apart,  covering  5  per  cent  of  the  total  area,  thus  crossing  it 
often  enough  to  get  representative  areas  under  all  conditions  of  moisture, 
shade,  exposure  (as  to  slope),  and  soil. 

The  belt  transect  shows  the  continuous  conditions  through  the  vege- 
tation of  a  formation  and  gives  graphically  the  relations  of  the  various 
aspects  and  situations.  It  furnishes  a  record  of  the  heterogeneity  of  the 
area  in  respect  to  species  and  soil  conditions.  The  transect  is  preferable 
to  the  plot  or  quadrat  in  most  instances,  because  the  quadrat  gives  only 
a  local  record,  and  does  not  give  topography  and  circumstances  leading 
from  one  homogeneous  formation  to  another. 

Notes  were  taken  on  the  kinds  of  soil,  whether  silt,  sandy,  rocky, 
clay,  etc.,  vegetation  cover,  condition  of  soil,  whether  mineral  or  covered 
with  humus,  duff,  or  litter,  and  amount  of  charred  logs  and  slash  on  the 
ground.  Number  and  age  of  each  species  of  seedlings  present  were  recorded 
with  conditions  under  which  each  individual  or  group  of  seedlings  was 
found,  as  to  soil,  shade,  or  protection  by  logs  or  slash. 

The  following  detailed  report  of  an  area  studied  in  northern  Idaho 
shows  the  methods  used: 

Designation Kaniksu-Fidelity  Lumber  Co.,  March  18,  1907. 

Location Sec.  26,  T.  57 N.,  R.  5W.,  Boise  M. 

Topography Rolling,  traversed  by  Pine  Creek— a  non-drivable  s 

and  the  West  Branch  River— a  drivable  stream,     blopes 
and  ravines  shown  by  map. 


PLATE  I 

The  Migration  Chart  shows  the  area  divided  into  units  having  similar  factors 
influencing  reproduction.  These  areas  are  designated  by  the  letters  of  the  alphabet. 
A  letter  appearing  on  two  or  three  areas  indicates  that  these  areas  are  similar. 

Areas  A,  B,  C,  and  D  are  all  within  seed  plots  under  about  50  per  cent  shade 
with  sparse  annuals  and  ground  cover  of  duff,  humus,  and  litter.  The  seed  trees  in 
the  plots  are  healthy  except  in  C  and  in  the  edge  of  D  where  they  have  been  badly 
damaged  by  fire. 

E  is  an  area  of  unburned,  partially  piled  slash  on  a  steep  north  slope  of  20  to  40 
per  cent,  with  scattered  small  trees  of  hemlock  and  cedar.  The  ground  cover  is  of 
sparse  annuals  and  patches  of  duff,  humus,  and  litter. 

F  is  an  area  of  unburned,  partially  piled  slash  on  a  southeast  slope  of  15  to  20 
per  cent.  The  ground  cover  consists  of  scattered  annuals,  and  a  large  per  cent  of 
the  soil  is  covered  with  litter  and  duff.  Scattered  trees  of  hemlock  and  small  cedar 
were  left  standing  on  this  area. 

G  is  practically  level.  The  greater  portion  of  it  is  unburned  slash,  partially 
piled,  and  the  northern  part  of  it  has  a  pole  stand  of  grand  fir  and  cedar.  The  ground 
cover  consists  of  a  few  annuals  and  litter  and  duff  with  some  exposed  places  of  mineral 
soil. 

H  is  a  south  and  west  slope  of  10  to  40  per  cent,  and  is  a  very  dry  and  hot  situa- 
tion. The  north  half  of  this  area  is  covered  with  slash,  piled  but  unburned.  The 
ground  is  covered  with  scattering  annuals  and  tufts  of  grass,  except  along  the  West 
Branch  River  where  there  is  a  heavy  cover  as  previously  described. 

J  is  the  general  broadcast  burned  area  of  flat  benches  and  slopes.  The  ground 
cover  is  described  in  the  general  description. 


PLATE  I 
Showing  the  migration  of  the  seed  from  the  seed  trees 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS 


Soil Silt  and  sandy  loam,  dry,  gravelly  on  hillsides. 

Condition  before  cutting.  Forest  mature  and  over-mature  consisting  of  two-age  classes 

of  100  years  and  200  years.     Considerable  fungus  and 

insect  injury. 


WHITB 
PINE 

WHITE 
LARCH 

5S 

CEDAR 

CEDAR 
POLES 

140 

140 

120 

120 

75 

Average  diameter  of  trees  (inches)  
Average  number  of  trees  per  acre  

20.1 
27.4 
17  564 

20.4 
3.7 
2  068 

20.4 
0.8 
358 

27.0 
2.8 
2  496 

12.8 
17 

545 

79 

11 

2  5 

7  5 

Seedlings  less  than  5  feet  high  per  acre  —  per 
cent  of  stand  
Trees  between  5  feet  high  and  6  inches  D.B.H. 

30 
10 

10 
2.5 

10 
2 

50 
16 

Number  trees  over  6  inches  D.B.H.  to  be  left 

4.5 

1.5 

0.5 

5.2 

Reproduction Hemlock  and  cedar  heavy  throughout.     White  pine  and 

larch  in  groups  in  openings. 
Utilization All   merchantable  timber,   living  and  dead,  standing  and 

down,  cut. 

Brush  disposal All  unmerchantable  timber,  slashed  and  broadcast,  burned. 

Burned-over June,  1910. 

Seed  years Good  seed  crop  in  1909  and  a  fair  crop  in  1911. 

Sylvicultural  system ....   Clear  cut  with  seed  plots. 
Condition  at  time  of  examination,  September  1912. 

Ground  cover.  Scattering  individuals  of  wild  rose  (Rosa),  bearberry 
(Arctostaphylos),  thimble  berry  (Rubus),  Solomon's  seal  (Polygonatum), 
fern  (Pteris),  fireweed  (Epilobium) ,  mountain  maple  (Acer),  willow  (Salix), 
service-berry  (Amelanchier) ,  vetchling  (Lathyrus),  thistle  (Carduus),  horse- 
tail (Equisetum),  lupine  (Lupinus),  alder  (Alnus),  goldenrod  (Solidago), 
spiraea,  lamb's  quarters  (Chenopodium) ,  various  kinds  of  grasses  in  tufts 
and  heavy  stands  on  river  bottom  flats,  and  clover  (Trijolium)  along  the 
road  sides,  make  a  ground  cover  of  about  50  per  cent.  This,  however,  is 
not  an  even  cover  as  the  vegetation  is  in  groups  with  many  open  or 
sparsely  covered  areas. 

The  areas  burned  over  are  quite  free  from  any  material  except  some 
scattered  charred  logs.  The  mineral  soil  is  exposed  in  some  places  and 
other  areas  are  covered  with  humus  and  duff.  Unburned  strips  covered 
with  pine  needles  and  wood  litter  occur  along  the  timber.  The  soil  has 
been  in  excellent  condition  for  reproduction  since  the  bum  of  1910,  and 
was  in  good  condition  at  the  time  of  the  examination. 

The  cut-over  area  as  a  whole  is  naturally  divided  into  units  which  have 
similar  factors  influencing  reproduction,  as  seed-plots,  slopes,  slash,  etc. 


6  JULIUS  VALENTINE  HOFMANN 

The  Migration  Chart  shows  that  the  reproduction  is  much  heavier  on 
all  of  the  areas  where  the  slash  was  left  unburned.  This  is  undoubtedly 
due  to  the  seed  and  seedlings  left  on  the  ground  at  the  time  of  cutting,  as 
there  are  no  seed  trees  in  the  vicinity  of  areas  E,  F,  and  G  to  reseed  them. 
All  of  the  burned  areas  adjoining  have  no  reproduction.  Areas  E,  F,  and 
G  have  seed  trees  of  cedar  and  hemlock,  but  no  white  pine. 

As  shown  by  the  Migration  Chart,  the  distance  of  seeding  from  the 
seed  trees  seldom  exceeds  2  chains. 

Conditions  where  the  seedlings  were  found  were  very  similar  to  the 
conditions  of  the  area  in  general,  indicating  that  no  seed  had  been  sown 
on  the  areas  farther  than  shown  by  the  Migration  Chart. 

These  points  were  borne  out  by  several  areas  studied  in  this  region. 
They  were  also  verified  by  intensive  studies  on  the  Yacolt  burn  of  1902, 
now  in  the  Columbia  National  Forest  in  Southern  Washington.  This 
burn  covers  over  600,000  acres,  and  areas  of  hundreds  of  acres  have  no 
green  trees  left. 

The  ^distance  of  seeding  to  produce  an  adequate  stand  of  seedlings,  500 
to  1,000  per  acre,  in  the  localities  studied  on  the  Yacolt  burn  was  found 
to  be  2  to  4  chains  for  Douglas  fir,  noble  fir,  and  amabilis  fir;  3  to  5 
chains  for  hemlock,  and  cedar;  and  usually  2  chains  for  white  pine. 

GERMINATION  OF  SEED 

The  length  of  time  the  seeds  of  a  species  require  for  germination  often 
determines  the  success  or  failure  of  that  species  on  certain  sites.  On  some 
sites  germination  conditions  are  favorable  for  only  a  short  period,  con- 
sequently in  order  to  take  advantage  of  such  periods  a  seed  must  germinate 
quickly.  Where  seeds  of  western  yellow  pine  germinate  in  eight  to  ten 
days,  the  seedlings  have  a  decided  advantage  over  the  western  white  pine, 
which  may  take  fifteen  to  twenty  days  or  more  to  germinate  under  the 
same  conditions.  In  situations  where  the  conditions  are  favorable  for 
only  three  or  four  weeks,  the  early  germinating  seed  assures  success  to  that 
species,  while  the  seed  which  germinated  slowly  may  be  only  beginning  to 
grow  when  unfavorable  conditions  occur,  with  a  consequent  loss  of  all 
germinating  seed  which  has  not  established  its  seedlings. 

On  the  other  hand,  the  habit  of  dormancy  may  prove  advantageous  to 
a  species  by  preserving  the  seed  until  a  favorable  season  stimulates  it  to 
growth.  By  the  refusal  to  respond  to  the  first  short  favorable  period  for 
germination,  the  following  drought  may  be  avoided.  Seeds  of  this  character 
are  often  early  spring  germinators  after  one,  two,  or  even  several  seasons 
of  storage.  This  characteristic  has  been  found  in  western  white  pine, 
Douglas  fir,  sugar  pine,  incense  cedar,  and  others.  When  these  species 
were  sown  in  the  nursery  or  seed  spotted  in  the  field,  the  germination 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  7 

continued  over  several  seasons.  Instances  of  field  sowing  of  Douglas 
fir  and  sugar  pine  have  been  found  where  the  results  were  considered  a 
failure  the  first  season  after  sowing,  and  some  germination  appeared  the 
second  season,  while  the  third  season  produced  a  very  satisfactory  germina- 
tion. While  this  may  occur  under  favorable  conditions  of  sowing,  the 
length  of  the  dormancy  period  in  nature  under  an  environment  less 
favorable  for  germination  is  still  further  prolonged. 

SIZE  OF  SEED 

That  the  early  development  of  the  seedling  is  dependent  on  the  food 
stored  in  the  endosperm  of  the  seed  was  shown  by  tests  of  seed  of  western 
yellow  pine,  Douglas  fir,  western  hemlock,  and  western  red  cedar,  in  sand, 
in  soil  to  which  nutrient  solutions  had  been  added,  and  in  potting  soil 
made  up  of  leaf  mold  and  sand.  The  following  nutrient  solution  was  used: 

To  each  liter  of  water  was  added: 

1 .      gram  calcium  nitrate 
0.25     "     potassium  chloride 
0.25     "     magnesium  sulphate 
0.25     "     acid  potassium  phosphate 

The  soil  was  moistened  with  this  solution  and  always  watered  with  the 
same  solution. 

The  seeds  germinated  equally  well  under  all  conditions,  but  the  dif- 
ferences were  very  soon  noticeable  after  germination. 

Seedlings  germinated  in  the  sand  came  above  the  ground  and  appeared 
as  good  as  those  grown  in  the  potting  soil  or  in  the  nutrient  solution.  When 
the  seed-coats  were  shed,  they  began  to  fail  and  apparently  were  unable 
to  get  any  nourishment,  or  at  least  not  sufficient  to  make  any  growth. 
After  the  cotyledon  stage,  these  seedlings  did  not  appear  healthy  and  many 
of  them  soon  developed  their  winter  or  resting  buds.  The  seedlings  in 
the  potting  soil  and  in  the  nutrient  solutions  made  good  growth  and  did 
not  develop  any  buds  until  they  had  passed  through  the  regular  growing 
period.  Those  grown  in  distilled  water  grew  until  the  food  contained  in 
the  seed  was  exhausted,  and  then  died. 

In  this  connection  it  was  noted  that  the  seedling  growth  the  first  season 
was  directly  proportional  to  the  size  of  the  seed.  This  fact  gives  species 
with  large  seeds  an  advantage  over  species  with  small  seeds,  for  example, 
yellow  pine  seedlings  would  become  established  on  dry  sites  where  hemlock 
or  cedar  would  fail.  The  yellow  pine  would  be  able  to  send  down  roots 
to  the  moist  soil,  due  to  the  food  stored  in  the  seed,  while  the  small-seeded 
species  would  have  to  depend  on  obtaining  nourishment  and  moisture 
from  the  surface  soil,  and  consequently  fail.  Table  I  shows  the  results 
of  experiments  with  different  depths  of  cover  in  loam  soil  to  determine 
the  influence  of  food  stored  in  the  endosperm. 


PLATE  II 

View  of  Yacolt  burn  of  1902,  on  the  Columbia  National  Forest  in  southern 
Washington,  showing  edge  of  the  green  timber  at  the  extreme  right  of  the  view;  no 
other  green  timber  in  sight.  This  is  part  of  the  area  where  the  reproduction  study 
was  made.  Looking  northwest  from  Lookout  Mountain. 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS 
TABLE   I 


SPECIES 

DEPTH  OF  COVER  — 
INCHES 

PER  CENT 
GERMINATED 

PER  CENT  APPEARED 
ABOVE  GROUND 

Pinits  ponder  osa  

1 

Pscudotsuga  taxifolia 

2 
3 
4 

\z 

83 
71 
36 

82 
74 
42 
0 

Tsuga  heterophylla  

V 

3 
4 

87 
72 
67 
42 
17 

Otf 

93 

85 
64 
50 
3 
0 

Thuya  plicata  

ix 

92 
86 
64 

42 

78 

vo 
76 
50 

5 
0 

70 

i 

1H 

64 
42 
25 
26 
19 

52 
24 
4 
0 
0 

The  above  table  shows  that  seedlings  will  grow  up  through  soil  a 
distance  which  is  in  direct  relation  to  the  size  of  the  seed.  The  develop- 
ment of  the  seedlings  showed  that  they  will  grow  to  a  size  which  is  in  direct 
relation  to  the  amount  of  nourishment  stored  in  the  seed.  If  the  seedling 
can  not  reach  the  surface  before  the  supply  of  nourishment  in  the  seed  is 
exhausted,  it  must  die.  On  the  other  hand  if  it  is  able  to  get  above  the 
ground,  even  as  a  final  effort,  the  cotyledons  open  up  at  once  and  turn 
green,  enabling  the  seedling  to  obtain  food  through  a  new  source,  viz.,  the: 
chlorophyll. 

It  follows  from  this  that  seed  may  often  germinate  when  covered  with 
litter  and  duff  and  the  seedling  may  not  reach  the  surface,  on  account  of 
the  size  of  seed  involved.  Here  then  the  larger-seeded  species  has  an 
advantage  over  the  smaller-seeded  species. 

The  occurrence  of  seedlings  or  trees  of  any  species  on  any  site  indicates 
that  the  site  is,  to  some  extent  at  least,  favorable  to  the  species  found  there, 
but  it  does  not  show  that  any  other  species  would  not  establish  itself  or 
develop  well  there  if  given  an  opportunity.  It  is  frequently  merely  a 
question  as  to  which  species  first  gets  possession  of  an  area  immediately 
after  the  virgin  forest  is  removed,  or  which  species  first  had  the  opportunity 
of  migrating  there.  In  other  instances  it  is  clearly  a  matter  of  competition 
between  species  as  to  their  ability  to  withstand  the  conditions  of  the  site- 
involved. 


10  JULIUS  VALENTINE  HOFMANN 

As  one  looks  at  the  peaceful  forest  one  should  remember  that  under- 
neath the  calm  serenity  of  the  scene  there  is  a  bitter  struggle,  a  relentless 
internecine  warfare  between  the  trees  already  established  there  and  those 
that  are  striving  to  enter  from  without. 

Soil  temperature,  soil  moisture,  aeration,  and  light  are  among  the 
ecological  factors  which  determine  the  establishment  of  a  forest  and  deter- 
mine the  types  within  a  forest.  A  wide  variation  of  any  one  of  these 
factors  on  different  sites  does  not  mean  that  the  varying  factor  is  the  one 
which  determines  the  type.  Other  factors,  varying  less,  but  approaching 
nearer  to  the  limit  of  favorable  conditions  would  have  a  greater  influence 
on  the  germination  of  the  seed  or  the  establishment  of  the  seedling.  All 
the  factors  must  be  taken  into  consideration,  and  also  the  limits  of  each 
under  which  the  seedlings  will  grow.  While  the  moisture  in  the  soil  in 
two  different  localities  may  be  equal,  the  soil  texture  may  have  a  decided 
influence  on  the  availability  of  the  moisture  for  plants;  that  is,  there  would 
be  a  decided  difference  in  the  wilting  coefficient.  The  fact  that  the  surface 
soil  often  dries  out,  while  at  a  depth  of  about  six  inches  moisture  may  be 
present  on  protected  slopes  and  absent  on  exposed  slopes,  gives  decided 
advantage  to  seedlings  with  deep  roots  formed  early  in  their  development. 
For  this  reason,  yellow  pine  has  an  advantage  over  hemlock  and  its  asso- 
ciates in  the  forests  of  western  Montana  and  Idaho.  For  the  same  reason, 
Douglas  fir  is  able  to  establish  itself  on  the  drier  slopes  of  the  Cascades, 
while  hemlock  and  cedar  fail.  A  south  slope  covered  with  yellow  pine  or 
Douglas  fir,  and  a  north  slope  covered  with  hemlock,  white  pine,  cedar,  and 
other  species,  does  not  mean  that  each  of  these  species  is  in  its  optimum 
habitat.  It  is  rather  a  question  of  competition  between  species  and  of 
establishment.  Yellow  pine  would  produce  excellent  forests  on  some  of 
the  slopes  occupied  by  other  species  if  it  could  establish  itself  there.  It  is, 
however,  crowded  out  by  the  large  number  of  seedlings  of  the  other  species. 
On  the  other  hand,  the  hemlock  and  cedar  do  very  well  under  the  conditions 
of  the  south  slopes  wherever  they  can  get  sufficient  moisture  to  establish 
themselves.  The  reason  these  species  are  not  in  mixture  all  through  the 
forest  is  not  due  to  a  lack  of  seed  or  even  to  the  germination  of  seeds  on 
the  different  slopes.  An  example  of  this  nature  was  noted  by  the  writer 
where  two  types  met  on  a  ridge.  The  south  slope  was  seeded  with  seed 
from  species  found  on  the  north  slope.  Seedlings  of  hemlock  and  cedar 
and  larch  were  found  germinating  along  with  those  of  Douglas  fir  and 
yellow  pine  in  the  spring  of  the  year,  but  in  the  fall  only  some  of  the  seed- 
lings of  yeUow  pine  and  Douglas  fir  were  left.  The  seedlings  of  the  other 
species  were  unable  to  live  through  the  dry  period  of  the  summer,  due  to 
their  small  roots  and  their  inability  to  reach  the  moist  layer  of  soil  below 
the  dry  surface  before  they  perished.  These  conditions  are  repeated  year 
after  year,  and  yet  the  type  remains  unchanged.  It  is  very  noticeable 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  11 

that,  wherever  a  ravine  or  spring  keeps  a  south  slope  moist,  seedlings  from 
the  species  of  the  north  slope  are  found. 

Different  slopes  often  get  about  the  same  amount  of  precipitation,  but 
there  is  such  a  marked  difference  in  the  evaporation  that  the  exposed 
slopes  dry  out  while  the  north  and  protected  slopes  remain  moist. 

The  effect  of  site  exposure  is  clearly  shown  by  the  following  summary 
table  of  meteorological  data  gathered  near  the  Wind  River  Experiment 
Station  at  a  station  on  a  south  slope,  at  an  elevation  of  2,150  feet,  one  on 
a  north  slope  at  an  elevation  of  1,750  feet,  and  one  on  an  intermediate 
flat  at  an  elevation  of  1,150  feet.  All  stations  were  in  the  same  watershed 
and  less  than  one-half  mile  apart. 

The  important  features  of  these  results  are  the  marked  differences  in 
evaporation  during  the  critical  drought  period.  During  August  the 
evaporation  from  water  surface  on  the  south  slope  was  15.1  inches,  while 
on  the  north  slope  it  was  only  1 . 8  inches,  with  a  corresponding  moisture 
content  of  the  surface  soil  on  the  south  slope  of  only  1.0  per  cent,  while 
the  north  slope  contained  6.5  per  cent.  With  this  extreme  dry  surface 
soil  on  the  south  slope,  there  still  remained  11.2  per  cent  of  moisture  at 
6  inches  deep  and  10.4  per  cent  at  12  inches.  This  would  support  plant 
growth  providing  a  large  enough  proportion  of  the  absorbing  root  systems 
were  contained  in  this  layer  of  soil. 

In  the  spring  of  1913,  100  seed-spots  of  Douglas  fir  were  sown  on  each 
of  the  sites,  south  slope,  north  slope,  and  flat,  and  25  per  cent  of  the  spots 
on  each  site  were  protected  by  cone-shaped  wire  screens  to  prevent  damage 
by  rodents. 

Three  examinations  were  made.  At  the  end  of  the  season  the  seed-spots 
on  the  south  slope  had  no  seedlings,  either  in  protected  or  unprotected 
spots,  since  all  that  germinated  during  the  season  died  in  the  dry  part  of 
the  summer.  On  the  north  slope  the  protected  spots  had  an  average  of 
.69  seedlings  per  spot,  and  44  per  cent  of  the  spots  contained  seedlings, 
while  the  unprotected  spots  averaged  .25  seedlings  per  spot  and  22  per 
cent  of  the  spots  had  seedlings.  On  the  north  slope  there  was  no  loss  of 
the  total  number  germinated.  On  the  flat  the  protected  seed-spots  averaged 
2 . 85  seedlings  per  spot  and  88  per  cent  of  the  spots  had  seedlings,  while 
the  unprotected  spots  averaged  .31  seedlings  per  spot  and  34  per  cent  of 
the  spots  contained  seedlings.  The  loss  of  the  total  germination  on  the 
flat  was  6  per  cent. 

In  the  spring  of  1913,  the  following  species  were  sown  under  wire  screens 
on  each  site:  Douglas  fir,  noble  fir,  western  white  pine,  and  western  yellow 
pine.  An  area  of  about  16  square  feet  was  sown  to  each  species,  one  half 
of  the  area  being  put  in  as  a  regular  seed-spot  and  the  other  half  broadcasted 
without  preparing  the  soil. 


TABLE  II 

SUMMARY  OF  METEOROLOGICAL  DATA  OF  STATIONS  ON  SOUTH  SLOPE,  NORTH  SLOPE, 

AND  PLAT 
Readings  averaged  by  months 


APRIL 

MAY 

JUNB 

JULY 

AUG. 

SEPT. 

OCT. 

Maximum  temperature  surface  soil 
South  slope  

82  0 

113  0 

109  2 

129  4 

101  5 

79  5 

North  slope  

71  0 

81  5 

77  2 

82  4 

63  5 

61  7 

Plat  

80  0 

109  5 

117  5 

139  2 

93  0 

69  5 

Minimum  temperature  surface  soil 
South  slope  

37  0 

46  0 

48  2 

46  8 

43  2 

38  2 

North  slope  

38  0 

48  7 

52  5 

51  0 

44  0 

37  5- 

Flat  

37  0 

47  7 

47  8 

45  0 

38  2 

33  7 

Set  maximum  temperature  surface 
South  slope  

46  0 

59  2 

63  2 

90  0 

121  0 

71  7 

56  Z 

North  slope  
Flat  

46.0 
44  0 

56.2 
60  0 

63.2 
69  7 

69.2 
92  2 

68.8 
104  6 

54.5 
75  7 

50.4 
56  5 

Soil  temperature  six  inches  deep 
South  slope  

45  0 

51  6 

60  5 

67  5 

73  4 

60  5 

52  2" 

North  slope  

43  0 

49  7 

58  6 

61  2 

63  4 

53  2 

50  0 

Flat 

45  0 

Soil  temperature  twelve  inches  deep 
South  slope. 

44  5 

50  9 

North  slope 

42  0 

Flat 

44  5 

Air  temperature 
South  slope  

43   0 

60  0 

55  0 

79  0 

North  slope  

46  0 

62  0 

61  0 

75  0 

Flat... 

44  0 

Relative  humidity 
South  slope. 

North  slope 

Flat  

Evaporation  from   water  surface   in 
inches 
South  slope. 

North  slope  . 

4.9 

Flat  

Per  cent  of  water  content  in  surface 
soil 
South  slope  

31  8 

North  slope  

Flat  

23  3 

Per  cent  of  water  content  in  soil  six 
inches  deep 
South  slope  

30  5 

North  slope  

35  9 

Flat  

26  3 

Per  cent  of  water  content  in  soil 
twelve  inches  deep 
South  slope  

31  5 

30.2- 

North  slope  

27  5 

31.8 

Plat  

28  4 

32.1 

30.7 

SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS 


13 


The  sowing  failed  on  the  south  slope.  A  few  seeds  germinated,  but  the 
seedlings  perished  during  the  dry  season.  The  noble  fir  did  remarkably 
well  on  the  north  slope,  and  the  Douglas  fir  and  white  pine  did  fairly  well, 
but  the  yellow  pine  failed.  There  was  no  loss  of  the  total  number  germi- 
nated. 

On  the  flat  the  Douglas  fir  did  very  well  and  had  a  15  per  cent  loss  of 
the  total  germination.  The  noble  fir  did  fairly  well,  with  a  loss  of  30  per 
cent  of  the  total  germination.  The  white  pine  germinated  very  little  and 
had  a  loss  of  46  per  cent  of  total  germination,  while  the  yellow  pine  germi- 
nated very  little,  and  15  per  cent  of  the  total  germination  died. 

The  conditions  under  which  the  seedlings  become  established  are  shown 
in  the  following  average  summary  of  four  areas  studied  in  northern  Idaho. 

TABLE  III 

CONDITIONS  UNDER  WHICH  SEEDLINGS  WERE  FOUND  ESTABLISHED 
IN  NORTHERN  IDAHO 


WHITE  PIKE 
PER  CENT 

CEDAR 
PER  CENT 

HEMLOCK 
PER  CENT 

LARCH 
PER  CENT 

GRAND  FIR 
PER  CENT 

SOIL 
On  humus  

3 

2 

7 

1 

9 

On  duff  

34 

16 

19 

32 

28 

On  wood  litter.  . 
On  mineral  soil.  . 
PROTECTION 
In  shade  
Under  logs  
In  open  
AGE 
1  year  old  

25 
38 

21 
8 
71 

37 

22 
60 

54 
4 
42 

74 

58 
16 

64 

8 
28 

87 

17 
50 

22 
8 
70 

25 

8 
55 

15 
25 
60 

2 

2  years  old  
3  years  old  
4  years  old  
5  years  old  

19 

34 
9 

1 

9 
16 

1 

8 
4 

1 

11 
55 
9 

4 
35 
50 
9 

In  regard  to  the  areas  examined,  the  above  tabulation  shows  that  the 
white  pine  seedlings  start  about  equally  well  on  the  duff,  wood  litter,  and 
mineral  soil,  while  the  other  species  do  not  show  any  particular  preference. 
In  this  study,  moisture  was  found  to  be  the  controlling  factor,  and  the 
other  conditions  recorded  are  usually  favorable  only  where  they  produced 
better  moisture  conditions. 

Effect  of  ground  cover  after  burns  or  cuttings.  An  area  was  selected  on 
a  south  slope  at  an  elevation  of  1,700  feet,  where  the  ground  cover  of  wild 
pea  vine  and  brush  was  very  dense.  One  square  rod  was  denuded  of  all 
vegetation  and  the  area  beside  it  left  untouched.  Readings  of  air  temper- 
ature at  the  height  of  the  crowns  of  seedlings,  and  soil  temperature  at 
surface,  6  inches  deep,  and  12  inches  deep  were  taken  each  week  on  the 
denuded  area  and  in  the  adjoining  -area  where  the  natural  vegetable  cover 


H 


JULIUS  VALENTINE  HOP  MANN 


was  undisturbed.     The  object  was  to  find  the  influence  of  ground  cover 
following  a  burn  or  clearing.     The  results  are  summed  tup  in  Table  IV. 


TABLE  IV 
NATURAL  COVER  AND  DENUDED  AREAS 


MAY 

JUNE 

JULY 

AUG. 

SEPT. 

OCT. 

AIR  TEMPERATURE 

60.8 

59.2 

70.7 

.86.6 

72.0 

55.7 

a     ,   . 

72.2 

64.4 

84.7 

102.8 

76.2 

60.0 

SOIL  TEMPERATURE 

Natural  rover   surface 

55.6 

56.0 

62.7 

73.4 

63.5 

56.2 

52  2 

55.2 

60.5 

68.4 

61.0 

54.5 

50  9 

55.0 

60.0 

66.4 

60.6 

54.5 

74  5 

67.5 

92.5 

124.2 

89.2 

64.5 

DC     d  d       inches  dee 

57  8 

62.0 

68.0 

78.7 

67.0 

54.2 

Denuded  12       "         " 

56  3 

61  5 

67.0 

74.4 

66.2 

56.2 

PER  CENT  SOIL  MOISTURE  CONTENT 

Natural  cover  surface  

33.3 

32.4 

23.1 

10.5 

33.4 

36.5 

Natural  cover,    6  inches  deep  

21.3 

26.7 

20.0 

12.9 

29.5 

26.5 

Natural  cover,  12       "        "    

23.9 

20.5 

18.6 

15.4 

28.4 

27.7 

11.0 

10.2 

4.1 

1.0 

12.7 

18.4 

26.7 

24.1 

22.5 

17.5 

24.2 

29.0 

Denuded  12       "         "    

23.2 

25.7 

21.1 

19.8 

27.2 

29.2 

•  Air  temperature  taken  at  crown  on  one-year-old  seedlings. 

Table  IV  shows  clearly  the  effect  of  evaporation  from  surface  soil  when 
denuded,  also  the  greater  per  cent  of  soil  moisture  at  the  6-inch  and  12-inch 
depths  as  compared  with  these  same  depths  in  the  area  having  the  natural 
ground  cover  of  wild  pea  vine  and  brush.  Although  the  surface  dried 
out  on  the  denuded  area,  the  6-inch  and  12-inch  depths  still  contained 
more  moisture  than  in  the  area  of  the  natural  cover,  due  to  the  moisture 
being  taken  out  of  the  soil  by  the  roots  and  evaporated  from  the  leaves  in 
the  area  under  natural  cover. 

The  hot,  dry  surface  soil  shown  in  Tables  II  and  IV  accounts  for  the 
loss  of  one-year-old  seedlings  on  these  exposed  slopes,  while  the  moist, 
cooler  surface  under  plant  cover  gives  the  young  seedlings  protection. 
The  greater  amount  of  moisture  in  the  6-inch  and  12-inch  depths  on  the 
denuded  area  and  exposed  slopes  also  shows  why  seedlings  with  deep  roots 
early  in  their  development  will  succeed  on  such  slopes. 

The  following  plates  show  the  size  of  seedlings  of  various  species  of 
conifers  up  to  one  year  of  age.  As  will  be  noticed  in  the  plates,  the  size 
of  the  seed  influences  directly  the  size  of  the  seedling  in  its  early  life. 


PLATE  III 

Pseudotsuga  laxijolia 

Douglas  fir 

(Size  %) 


/f, 


PLATE  IV 

Abies  nobilis 

Noble  fir 

(Size  M) 


PLATE  V 

Pinus  monticola 

Western  white  pine 

(Size  X) 


12 


PLATE  VI 

Pinus  slrobus 

Eastern  white  pine 

(Size  %} 


II 


A     B 


r 


\ 


PLATE  VII 

Pinus  resinosa 

Norway  pine 

(Size  «) 


PLATE  VIII 

Pinus  divaricala 

Jack   pine 

(Size  «) 


PLATE  IX 

Pinus  lambertiana 

Sugar  pine 

(Size  ft) 


B 


PLATE  X 

Tsuga  mertensiana 

Mountain  hemlock 

(Size  JO 


PLATE  XI 

Thuya  plicata 

Western  red  cedar 

(Size  5/6) 


DESCRIPTION  OF  PLATES 
PLATE  III 

A.  Seed.     Color:  light  reddish  to  a  dark  brown  and  lustrous  above,  pale  white  mottled 

with  brown  below,  smooth. 

Size:  4-6  mm.  long;  2.5-4  mm.  wide  at  the  widest  point,  tapering  to  a  point 
opposite  wing.  Wings  dark  brown,  6-8  mm.  long,  3-4  mm.  wide  at 
widest  part  just  below  the  middle,  tapering  to  a  rounding  apex. 

Weight:  average  35,000  seeds  per  pound. 

B.  Seedling  as  it  appears  above  ground,  about  to  shed  seed-coat.     Hypocotyl  green 

to  reddish  tinge,  cotyledons  green. 

C.  Seedlings  with  cotyledons;  green.     Cotyledons  1.5-2.5  cm.  long;  linear  tapering 

point;  6-9  in  number. 

D.  Seedling  one  year  old.     Showing  remarkable  root  system  adapting  it  to  the  drier 

slopes  and  causing  unusually  fast  growth. 

PLATE  IV 

A.  Seed.     Color:   pale  reddish  brown,   slight  tendency  to  be  glossy.     Wing  very 

slightly  lighter  brown  than  the  seed. 

Size:  10-12  mm.  long,  5-6  mm.  wide  at  widest  part  near  wing.  Tapering  to 
a  point.  Wing  10-15  mm.  long,  12—15  mm.  wide  with  widest  part  at 
top  and  forming  a  triangular  shape  with  seed.  Top  also  truncate. 

Weight:  25,000  per  pound. 

B.  Seedling  as  it  appears  above  ground,  about  ready  to  shed  seed-coat.     Hypocotyl 

reddish  green.     Cotyledons  green. 

C.  Seedlings  in  cotyledon  stage.     Cotyledons  2-3  cm.  long,  4-7  in  number,  usually  6. 

Long  slender,  tapering  point. 

D.  One-year-old  seedling.     A  well  developed  plant. 

PLATE  V 

A.  Seed.     Color:  pale  reddish  brown,  mottled  with  black. 

Size:  5-7  mm.  long,  4-5  mm.  wide  at  widest  part;  oblong  to  triangular  in 
shape.  Wings  light  brown,  1.5-2.5  cm.  long,  5-7  mm.  wide  at  widest 
point,  just  above  the  middle.  Rapid  taper  from  widest  point  to  a 
rounded  apex. 

Weight:  average  30,000  seeds  per  pound. 

B.  Seedling  as  it  appears  above  ground;  green — sometimes  pinkish,  about  to  shed 

seed-coat. 

C.  Seedling  with  cotyledons.     Cotyledons  2-2.5  cm.  long,  6-9  in  number,  tapering 

point. 

D.  Seedlings  one  year  old,   showing  strong  root  system  enabling  the  seedling  to 

establish  itself.     True  leaves  in  bundles  of  5  do  not  appear  until  second 
season. 


PLATE  VI 

A.  Seed.     Color:   reddish   brown,   sometimes  lighter   brown   mottled   with   black. 

Wings  dark  brown. 
Size:  5-6  mm.  long,  3-4  mm.  wide  at  widest  part,  oval  to  triangular  shaped. 

Wings   1-1 . 5  cm.  long,  5-6  mm.   wide  just  above  seed  and  tapering 

gradually  to  an  almost  pointed  apex. 
Weight:  35,000  per  pound. 

B.  Seedling  as  it  appears  above  ground,  about  to  shed  seed-coat. 

C.  Seedlings  with  cotyledons.     Stem  pinkish  green.     Cotyledons   1.2-2  cm.  long, 

linear  with  tapering  point. 

D.  Seedling  one  year  old.     True  leaves  in  bundles  of  5  do  not  appear  until  second 

year.     Seedling  well  established  at  end  of  first  season. 

PLATE  VII 

A.  Seed.     Color:  dull  chestnut  brown,  mottled  with  grey.     Wings  lighter  brown 

with  strips  of  darker  brown. 
Size:  4-5  mm.  long,   2.5-3  mm.  wide,  almost  round  and  oblong.     Wings 

1-1 . 5  cm.  long  and  .  5- .  7  cm.  wide  at  widest  part  near  middle,  tapering 

to  oblique  rounded  point. 
Weight:  60,000  per  pound. 

B.  Seedling  as  it  appears  above  ground,  about  to  shed  seed-coat.     Pinkish  stem. 

C.  Seedling  with  cotyledons.     Stem  pinkish  color.     Cotyledons  green,  linear  2—2.5 

cm.  long  tapering  point.     5  to  7  in  number,  usually  6. 

D.  Seedling  one  year  old,  showing  that  it  is  well  established  at  this  age. 

PLATE  VIII 

A.  Seed.     Color:  almost  black,  dull  brown  spots.     Wings  very  light  brown  with 

darker  brown  stripes  and  margin. 
Size:  4  mm.  long,  2  mm.  wide  at  widest  part,  triangular  in  shape.     Wings 

8  mm.  to  1  cm.  long,  3-4  mm.  wide  at  widest  part  near  middle,  broad 

rounded  apex. 
Weight:  120,000  per  pound. 

B.  Seedlings  as  they  appear  above  ground,  about  to  shed  seed-coat.     Hypocotyl 

pale  pink. 

C.  Seedlings  with  cotyledons.     Cotyledons  1.2-1.8  cm.  long,  narrow  long  tapering 

point,  green.     4-7  in  number. 

D.  Seedling  one  year  old.     Well  established  as  shown  by  root  system. 


PLATE  IX 

A.  Seed.     Color:  dark  brown,  shiny  on  one  side — side  next  to  cone — and  a  greyish 

brown  on  other  side.     Wings  dark  brown. 
Size:   1-1.5  cm.  long,   1-1.2  cm.  wide.     Very  thick,  oblong  to  triangular 

shape.     Wings  1.5-1.8  cm.  long,  1.5  cm.  wide.     Widest  at  top  with 

very  slightly  rounded  top. 
Weight:  2,370  per  pound. 

B.  Germinated  seed  just   as   seed-coat  pushes  above   ground,   showing   deep   root 

developed. 

C.  and  D.     Seedlings    one   year    old.     Well    developed    root    systems.     Cotyledons 

3.5-4    cm.    long.     Green,    12—16    in    number,    tapering    point.     Stem 
reddish  green.     True  leaves  in  bundles  of  5  do  not  appear  until  second 


PLATE  X 

A.  Seed.     Color:  brown  to  deep  reddish  brown.     Wings  pale  brown  merging  to  a 

reddish  brown  where  wing  is  attached  to  seed. 
Size:  2  mm.  wide,  5  mm.  long,  triangular  shaped.     Wing  5-6  mm.  wide  at 

widest  part  near  top.     1  cm.  long.     About  equal  width  throughout  with 

broad  rounded  apex. 
Weight:  260,000  per  pound. 

B.  Seedlings  as  they  appear  above  ground.     Hypocotyl  reddish  tinge.     Cotyledons 

pale  green. 

C.  Seedlings  with  cotyledons.     Cotyledons  4-5  mm.  long,  linear  with  short  tapering 

points.     Midrib  not  as  distinctive  as  in   Tsuga  heterophylla.    3-5  in 
number,  usually  3  or  4. 

D.  Seedling  one  year  old. 

PLATE  XI 

A.  Seed.     Dry.     Color:  brown  with  lighter  brown  wings. 

Size:  3  mm.  long,  narrow;  wings  4  mm.  long  and  3  mm.  wide  including  wings. 

Wings  usually  unequal,  forming  obcordate  apex  with  seed. 
Weight:  220,000  per  pound. 

B.  Seedling  with  cotyledons.     Hypocotyl  pale  pink  color;  cotyledons  linear  6  mm. 

long,  green,  two  in  number. 

C.  Seedling  one  year  old. 

D.  Seedling  three  years  old.     First  true  leaves  forming.     This  shows  that  it  takes 

the  seedling  a  long  time  to  establish  itself  and  that  it  must  have  favor- 
able conditions  for  more  than  one  season. 


!8  JULIUS  VALENTINE  HOFMANN 

A  study  of  the  foregoing  plates  will  show  the  nature'  of  the  early 
development  of  these  species.  The  noticeable  thing  is  that  the  species 
which  require  the  greatest  amount  of  moisture  are  the  ones  in  which  the 
seedlings  are  slow  in  establishing  themselves.  The  natural  result  of  this 
is  that  these  species  are  always  found  near  the  streams  and  on  moist  slopes. 
Cedar  requires  about  three  years  to  establish  its  seedlings,  while  a  sugar 
pine  or  Douglas  fir  seedling  is  well  established  at  the  end  of  the  first  season. 
Hemlock  is  another  example  of  a  species  with  a  small  seedling  during  the 
first  year,  although  it  will  produce  a  greater  height  growth  than  its  asso- 
ciates after  the  seedling  is  established,  that  is,  after  the  third  or  fourth  year. 
It  is  clearly  seen  also  that  species  which  have  large  seeds  establish  their 
seedlings  early,  enabling  them  to  live  in  places  unfavorable  to  smaller- 
seeded  species. 

VIABILITY  OF  SEED 
SEEDS  TREATED  WITH  CHEMICALS 

The  following  experiments  for  viability  tests  of  the  seed  of  Pinus 
monticola  showed  that  the  seed  will  stand  rigorous  treatment  and  still 
germinate.  No  attempt  was  made  to  duplicate  conditions  as  they  might 
exist  in  the  litter  and  duff  on  the  forest  floor,  but  rather  to  test  out  the 
limit  of  endurance  of  the  seed. 

Copper  acetate.  Five  treatments  were  given  varying  in  strength  from 
four  ounces  to  thirty-two  ounces  of  copper  acetate  per  gallon  of  water  in 
which  the  seed  was  soaked  for  two  hours.  Germination  was  not  affected 
and  gave  the  same  results  as  the  untreated  plot. 

Six  treatments  with  strengths  varying  from  two  to  four  ounces  per 
gallon  of  water  in  which  the  seed  was  soaked  from  twelve  to  twenty-four 
hours  showed  no  effect  on  the  germination.  Traces  of,  blue  coloring  in 
the  endosperm  of  all  of  the  treated  seed  showed  that  the  solution  had 
penetrated  the  seed-coats.  This  coloring  was  quite  noticeable  in  the  use 
of  the  stronger  treatments.  Some  of  the  more  strongly  treated  plots 
gave  as  good  germination  as  those  untreated,  showing  that  the  vitality  of 
the  seed  was  unimpaired.  The  seedlings  that  came  up  were  thrifty  and 
the  root  systems  were  well  developed. 

Zinc  chloride.  Eight  treatments  were  used  varying  in  strength  from 
two  ounces  of  zinc  chloride  to  one  gallon  of  water,  up  to  sixty  ounces  of 
zinc  chloride  to  one  gallon  of  water.  Seed  soaked  for  two  hours  showed 
no  effect  on  germination. 

Four  treatments,  from  ^  to  one  ounce  of  zinc  chloride  to  one  gallon  of 
water  applied  to  seed  for  thirty  minutes,  did  not  affect  germination. 

Ten  treatments,  varying  from  one  part  of  zinc  chloride  to  fifty  parts 
of  water  by  weight,  up  to  one  part  zinc  chloride  to  five  hundred  parts 
water;  and  ten  treatments,  varying  from  one  part  zinc  chloride  to  three 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS 


19 


parts  of  water  by  weight,  to  one  part  of  zinc  chloride  to  forty  parts  of 
water,  all  showed  no  influence  on  the  germination.  Zinc  chloride  has 
been  found  to  be  a  stimulant  to  germination  in  the  work  done  in  soil  treat- 
ment for  fungi,  and  was  expected  to  be  a  stimulant  in  germinating  the 
white  pine  seed,  but  such  did  not  prove  to  be  the  case. 

Ether.  Seven  treatments  of  ether,  varying  from  dipping  to  exposing 
the  seed  to  the  ether  fumes  for  four  hours,  showed  that  the  seeds  were  killed 
if  left  in  the  fumes  for  more  than  one  hour.  Liquid  ether  was  put  into  a 
bottle  and  the  seed  suspended  above  it  on  a  gauze,  thus  subjecting  the  seed 
to  the  ether  fumes.  The  bottle  was  closed  with  an  air-tight  glass  stopper. 

Seed  soaked  in  water.  Seed  was  put  into  water  at  the  following  tem- 
perature in  degrees  Fahrenheit  and  left  for  forty  hours:  100,  110,  120, 
130,  140,  150,  160,  170,  180,  190,  200,  212.  The  temperature  of  the  water 
was  65°  to  70°  F.  when  the  seed  was  taken  out.  No  germination  was 
obtained  above  150°  F.,  but  the  seed  soaked  in  140°  germinated  10  per 
cent  as  compared  with  4  per  cent  in  the  unsoaked  seed,  showing  that  this 
temperature  had  stimulated  germination. 

Sulphuric  acid.  The  following  table  shows  the  results  of  treatments 
of  western  white  pine  seed  with  sulphuric  acid. 

TABLE  V 


TREATMENT 
OF  SEED 

NUMBER  DAYS 
BEFORE  FIRST 
GERMINATION 

GERMINATION 
PER  CENT 
15  DAYS 
AFTER  FIRST 
GERMINATION 
IN  SERIES 

GERMINATION 
PER  CENT 
50  DAYS  AFTER 
PLANTING 

CONDITION  OF  SEED 
WHBN  PLANTED 

Dipped  A 

23 

2.8 

4.0 

Exocarp   charred  by 
acid 

F-A-5 

19 

3.2 

5.0 

Exocarp   charred  by 

acid 

F-A-10 

26 

1.6 

3.2 

Exocarp    and    meso- 

carp  charred 

F-A-15 

19 

1.6 

3.2 

Exocarp    and    meso- 

carp  charred 

F-A-30 

23 

1.2 

3.0 

Exocarp    and    meso- 

carp  charred 

F-A-45 

19 

2.4 

7.4 

Exocarp    nearly    re- 

moved  and   meso- 

carp  and  endocarp 

charred 

Untreated 

26 

1.0 

2.0 

Normal 

Untreated 
H-A-30 

21 
21 

1.2 

1.6 

2.0 
3.2 

Normal 
Not  discolored,  seed- 

coats  intact 

K-A-60 

21 

1.6 

3.4 

Not  discolored,  seed- 
coats  intact 

M-A-120 

37 

0.0 

2.0 

Not  discolored,  seed- 
coats  intact 

H-A-180 

21 

0.8 

2.2 

Not  discolored,  seed- 
coats  intact 

A         =  Commercial  sulphuric  acid. 

F-A-5=Seed  soaked  in  acid,  full  strength,  for  5  minutes,  etc. 

H-A  =  One-half  strength  acid,  that  is,  equal  parts  with  water. 


PLATE  XII 

View  on  Oregon  National  Forest  in  northern  Oregon  showing  the  results  of  a 
second  fire.  This  area  was  burned  over  in  1902  and  followed  by  dense  reproduction 
of  Douglas  fir,  noble  fir,  hemlock,  and  cedar.  The  second  fire  ran  through  in  1909. 
Note  that  the  second  fire  is  not  followed  by  reproduction. 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  21 

Commercial  sulphuric  acid  chars  the  seed-coats  as  soon  as  the  seed  is 
immersed.  Where  the  seeds  were  left  for  thirty  minutes  and  more  in  the 
full  strength  acid,  the  seed-coats  could  all  be  removed  by  slightly  rubbing 
the  seed,  thus  leaving  the  endosperm  naked.  Even  in  this  condition,  the 
viability  of  the  seed  was  unimpaired,  and,  as  the  table  shows,  the  strongest 
treatment  gave  the  best  germination  results. 

Seed  treated  with  half  strength  acid  showed  no  appreciable  effects 
upon  the  seeds  or  on  the  germination. 

Germination  in  all  of  the  plots  was  perfectly  normal.  Seedlings  in  all 
the  treatments  appeared  healthy  and  thrifty.  Seedlings  in  the  plots 
treated  with  the  full  strength  acid  for  the  longer  periods  appeared  above 
ground,  bringing  up  the  endosperm  without  the  seed-coat,  and  in  some 
cases  the  cotyledons  grew  out  through  the  sides  of  the  endosperm.  Seed- 
lings appearing  in  this  way  produced  strong,  vigorous  plants  however. 

Seed  that  was  soaked  in  C.  P.  sulphuric  acid  for  one  hour  was  covered 
with  water  after  the  acid  was  poured  off.  The  reaction  created  a  tempera- 
ture of  168°  F.  The  exocarp  was  charred  and  most  of  it  destroyed  by 
the  acid.  The  mesocarp  and  endocarp  were  also  charred  so  that  they 
rubbed  off  easily,  but  the  endosperm  or  food  material  of  the  seed  was 
apparently  uninjured.  Some  of  the  seed  germinated.  Seed  soaked  for 
more  than  one  hour  and  treated  with  water  failed  to  germinate. 

Aside  from  the  experiments  made  to  test  out  what  severe  conditions 
seeds  will  withstand  and  still  retain  their  viability,  the  following  chemical 
experiments  to  determine  influence  on  germination  were  done  with  the  same 
species,  Pinus  monticola. 

Copper  sulphate.  Ten  treatments,  varying  from  one  part  copper 
sulphate  to  one  part  of  water  by  weight,  up  to  one  part  copper  sulphate 
to  five  and  one-half  parts  of  water,  showed  that  germination  was  stimulated 
by  the  chemical.  The  seed-coats  opened  in  a  few  days,  but  as  soon  as 
they  separated  the  copper  sulphate  solution  stained  and  killed  the  germi- 
nating seed. 

Copper  acetate.  Ten  treatments,  varying  from  one  part  copper  acetate 
to  one  part  water  by  weight,  to  one  part  copper  acetate  to  five  and  one-half 
parts  of  water,  showed  that  germination  was  stimulated  by  the  copper 
acetate,  but  the  growing  tips  were  killed  as  soon  as  they  appeared.  Chemi- 
cal injury  occurred  in  all  of  the  strengths  used.  In  the  weaker  treatments, 
the  germinating  tips  were  stained  blue,  and  in  the  stronger  treatments 
the  entire  endosperm  and  plumule  were  stained  blue. 

The  above  experiments  show  that  the  seed  in  the  dormant  state  will  with- 
stand very  severe  conditions,  but  is  quite  easily  killed  after  germination 
begins.  The  chemical  condition  of  the  forest  floor  may  therefore  influence 
the  viability  of  the  seed  and  also  be  a  major  factor  in  determining  the  length 
of  the  period  through  which  the  seed  will  lie  dormant  and  retain  its  viability. 


22  JULIUS  VALENTINE  HOFMANN 

It  is  known  that  seeds  of  other  plants  are  viable  for  long  periods,  and 
the  writer  has  known  wild  oat  seed  (Avena  fatua)  to  remain  in  soil  for 
seven  years  and  produce  a  good  germination  the  year  it  was  plowed  up. 

Becker2  draws  the  conclusion  that  oxygen  acts  as  a  stimulant  in  seed 
germination,  and  many  of  the  conditions  under  which  the  seed  germinates 
or  does  not  germinate  seem  to  bear  this  out. 

Hatfield's3  work  on  the  Vitality  of  Seed  showed  that  the  Hibiscus 
militaris  germinated  after  ten  years,  Rocky  Mountain  columbine  after 
six  years,  tobacco,  verbenas,  ageratum,  after  several  years'  storage. 

Duval4  found  the  following  seeds  germinated  after  being  buried  in 
layers  of  clay,  not  below  the  frost  line,  for  three  and  a  half  years :  Trifolium 
pratense,  Trifolium  repens,  Polygonum  avariculare,  Bursa  pastoris,  Anthemis 
cotula.  The  soil  was  taken  into  the  greenhouse  and  the  seed  germinated. 

Beal5  secured  some  germination  from  the  following  seeds  after  they 
had  been  stored  in  soil  for  twenty  years:  Amaranthus  retroflexus,  Brassica 
nigra,  Capsella,  Bursa  pastoris,  Lepidium  virginicum,  Anthemis  cotula, 
Malva  rotundafolia,  Rumex  crispus,  Verbascum  thapsus,  Stellaria  media, 
Polygonum  hydropiper. 

These  experiments  give  some  idea  as  to  the  viability  of  the  seed  of 
some  of  the  common  and  well-known  weeds.  Most  of  these  have  seeds 
with  very  thin  seed-coats  that  are  easily  soaked  with  water.  It  is  very 
probable  that  seed  of  the  conifers  with  more  or  less  resinous  seed-coats 
would  remain  viable  for  a  longer  period.  The  characteristics  of  some  of 
the  coniferous  seeds  are  well  known,  such  as  the  western  white  pine, 
Douglas  fir,  eastern  white  pine,  and  the  junipers.  The  seeds  of  these  will 
often  not  germinate  for  two  or  three  years  even  under  the  best  of  con- 
ditions in  the  nursery.  Certainly  they  will  remain  viable  as  long  or  even 
longer  when  in  the  forest  floor  under  unfavorable  germinating  conditions, 
but  at  the  same  time  under  good  storage  conditions. 

Conzet6  showed  that  the  seed  of  the  Norway  pine  (Pinus  resinosd) 
remained  in  the  forest  floor  for  three  years  and  then  produced  good  germi- 
nation. 

The  results  of  the  study  of  the  Yacolt  burn  are  a  practical  demonstra- 
tion of  the  viability  of  coniferous  tree  seeds.  The  study  showed  that 
reproduction  occurs  over  the  entire  burn.  The  seedlings  which  germi- 
nated from  one  to  three  years  after  the  fire  vary  in  density,  regardless 
of  the  location  of  seed  trees,  while  the  seedlings  germinating  later  than  this 

*H.  Becker,  Uber  die  Keinung  verschieden  artiger  Fruchte  und  Samen  bei  derselber  Species. 
Beihefte  Botanisches  Centralblatt  29:21-143.  1912. 

1  T.  D.  Hatfield,  Vitality  of  seed.     Garden  and  Forest  p.  297.     1897. 

4  Duval,  in  the  Botanical  Gazette     37:146-47.     1904. 

5  Beal,  Vitality  of  seeds.     Botanical  Gazette     37:222.     1904. 

*  G.  M.  Conzet,  A  qualitative  and  quantitative  study  of  the  seed  production  and  reproduction  of 
Norway  pine  (Pinus  resinosa).  Master's  thesis,  the  University  of  Minnesota.  ,  1913. 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  23 

are  almost  all  in  close  proximity  to  seed  trees.  At  a  distance  of  one  or 
two  miles  from  seed  trees,  the  reproduction  was  in  many  instances  much 
more  dense  than  it  was  near  the  trees,  often  reaching  20,000  to  30,000 
seedlings  per  acre.  The  distance  from  the  seed  trees  and  the  erratic 
occurrence  of  the  dense  stands  of  seedlings,  sometimes  near  seed  trees 
and  sometimes  at  great  distances  from  them,  showed  that  the  seed  had 
not  been  blown  in  by  the  wind  since  the  fire.  The  areas  of  dense  stands 
of  reproduction  ending  in  very  irregular  edges,  beyond  which  no  repro- 
duction occurred,  were  convincing  evidence  that  the  seed  producing  the 
stands  was  present  before  the  fire.  These  irregular  edges  showed  where 
the  ground  fire  which  consumed  all  the  duff  had  died  out.  Where  the 
duff  was  left  unburned  the  reproduction  occurred.  In  all  cases  where 
reproduction  occurred  in  burns,  the  burned  trees  of  the  species  comprising 
the  reproduction  were  found  in  the  immediate  vicinity. 

When  the  Yacolt  fire  occurred  in  the  early  part  of  September,  1902, 
all  of  the  timber  was  killed  and  the  seed  of  that  year's  crop  was  badly 
scorched  or  burned.  This  is  shown  by  the  fact  that  there  were  no  unburned 
cones  or  cone  scales  present  on  the  burned-over  areas,  while  charred  cones 
and  cone  scales,  as  well  as  seeds  of  all  of  the  species  burned,  were  found. 
Also  in  the  places  where  the  surface  of  the  litter  and  duff  was  charred, 
but  undisturbed  since  the  fire,  seeds  were  found  buried  in  the  duff,  some 
of  which  still  had  perfect  wings.  These  facts  are  further  strengthened 
by  the  appearance  of  the  clear-cut  margins  and  abrupt  endings  of  the 
areas  of  good  reproduction  where  30,000  or  more  seedlings  per  acre  occur, 
showing  that  the  seed  was  in  the  litter  and  duff,  and  lived  through  the  fire. 
That  a  large  per  cent  of  this  seed  germinated  during  the  first  season  is 
shown  by  the  large  percentage  of  eleven-year-old  seedlings.  The  five  to 
ten  year  age  class  showed  the  distribution  of  the  seedlings  that  came 
from  the  seed  which  germinated  some  years  after  the  fire.  Those  of  the 
older  age  classes  at  great  distances  from  the  seed  trees,  undoubtedly  came 
from  the  seed  which  had  remained  dormant  in  the  litter  or  duff  and  escaped 
the  fire,  as  usually  no  seedlings  under  five  years  of  age  were  found  in  these 
localities.  In  the  case  of  the  western  white  pine,  there  were  no  seedlings 
under  five  years  old  found  during  the  entire  study,  although  older  white 
pine  seedlings  were  distributed  over  the  entire  area.  This  indicated  that 
the  white  pine  seeds  remained  viable  for  six  years  under  the  conditions 
to  which  they  were  exposed.  White  pine  seeds  were  found  in  some  of 
the  charred  cones  and  also  some  in  the  litter  and  duff,  but  these  undoubtedly 
were  killed  by  the  fire  or  were  not  viable. 

The  fire  advanced  before  a  southeast  wind  and  the  effects  of  it  are 
recorded  in  the  sparse  reproduction  on  the  south  and  southeast  slopes 
where  the  fire  was  hottest  and  where  all  of  the  litter  and  duff  was  burned. 
On  these  slopes  there  were  no  areas  of  reproduction,  only  occasional 

398316 


24  JULIUS  VALENTINE  HOP  MANN 

scattered  seedlings,  showing  that  very  little  seed  was  left  after  the  fire, 
while  on  the  slopes  not  struck  by  the  direct  flames  of  the  fire,  reproduction 
occurs  in  very  dense  stands  regardless  of  the  distance  from  seed  trees. 

Reproduction  was  found  at  distances  of  one  or  two  miles  from  the 
nearest  seed  trees.  In  the  case  of  the  white  pine,  there  are  no  seed  trees 
on  the  township  that  could  have  any  influence  whatever  on  the  area  over 
which  the  reproduction  of  this  species  extends.  Without  a  doubt  the  seed 
was  there  before  the  fire  passed  over  the  area,  and  escaped  destruction. 
This  seed  may  have  dropped  from  the  trees  the  year  previous  to  the  fire 
or  even  earlier,  as  must  be  the  case  where  heavy  stands  of  reproduction 
appear  during  the  first  season  following  the  fire,  since  a  dense  stand  of 
reproduction  is  not  due  to  a  single  crop  of  seed  but  rather  to  an  accumu- 
lative crop  of  several  years.  If  the  seed  produced  the  same  year  the  fire 
passed  over  the  area  was  not  killed,  this  study  shows  that  this  seed  must 
lie  dormant  in  the  forest  floor  for  several  years.  The  indications  are  that 
the  white  pine  remained  six  years;  Douglas  fir,  six  years;  noble  fir,  three 
years;  amabilis  fir,  five  years;  hemlock,  three  years;  and  yew  was  found 
scattered  over  the  typical  slopes  of  this  species,  varying  in  years  from 
eleven  to  three,  showing  that  the  seed  remained  dormant  for  eight  years. 
The  yew  was  a  good  index  in  accounting  for  the  seed  on  the  area,  as  there 
is  no  question  about  the  wind  distribution  of  the  berry-like  seed.  The 
theory  that  animals  carried  the  seed  can  not  be  accepted  because  the 
seedlings  invariably  appear  among  the  burned  snags  of  yew,  whereas 
animal  distribution  would  not  be  confined  to  these  areas. 

These  conditions  are  duplicated  on  all  of  the  burns  gone  over  on  the 
Snoqualmie  National  Forest  in  northern  Washington  and  the  Oregon 
National  Forest  in  northern  Oregon.  The  burns  on  these  forests  were 
not  studied,  but  general  observations  indicated  that  the  conditions  were 
the  same  as  those  found  on  the  Columbia.  The  noticeable  feature  here 
was  the  absolute  lack  of  reproduction  after  a  second  fire  except  very  near 
to  seed  trees.  This  fact  shows  that  good  and  wide-spread  reproduction 
following  a  first  burn  comes  from  seed  stored  in  the  forest  floor,  and  can 
not  be  attributed  to  seed  furnished  by  a  few  surviving  trees.  Single 
seed  trees  surviving  a  second  fire  never  restock  an  area  except  in  their 
immediate  vicinity.  If  a  few  escaped  trees  could  restock  a  burn  they 
would  also  restock  a  second  burn  on  the  same  area. 

SUMMARY  AND  CONCLUSIONS 

All  forest  tree  species  in  forest  stands  produce  sufficient  seed  to 
reestablish  their  own  type  under  favorable  conditions,  and  a  change  of 
type  or  removal  of  a  forest  from  any  area  once  covered  with  a  forest  is 
due  to  other  factors  than  production  of  seed. 


SEED  CHARACTERISTICS  IN  CONIFEROUS  FORESTS  25 

Species  producing  large  seeds  produce  comparatively  few  in  number. 

Seed  distribution  is  one  of  the  important  factors  controlling  the  estab- 
lishment of  a  forest  type. 

In  the  white  pine  region  of  Idaho,  reproduction  by  wind-blown  seed 
can  not  be  depended  upon  for  more  than  150  feet  from  the  seed  trees. 

In  the  Douglas  fir  region  of  the  Cascades  along  the  Columbia  River, 
reproduction  by  wind-blown  seed  of  Douglas  fir  and  its  associates  can  not 
be  depended  upon  for  more  than  about  300  feet  from  the  seed  trees. 

Germination  conditions  are  often  unfavorable  in  a  shaded  and  cool 
forest  floor,  hence  seed  may  lie  dormant  for  long  periods. 

By  the  removal  of  a  forest,  germinating  conditions  are  improved, 
and  the  dormant  seed  germinates. 

Moisture  is  the  chief  factor  in  the  establishment  of  the  seedling,  while 
temperature  is  often  a  more  important  factor  in  germination. 

The  size  of  the  seedling  during  its  early  life  is  directly  proportional 
to  the  size  of  the  seed. 

A  seedling  from  a  large  seed  becomes  permanently  established  much 
earlier  than  a  seedling  grown  from  a  small  seed,  hence  the  former  is  able 
to  obtain  and  hold  possession  of  the  more  unfavorable  sites. 

Seed  is  always  present  in  the  forest  floor,  generally  covered  with  and 
mixed  in  a  layer  of  litter  and  duff. 

This  seed  is  a  source  of  reproduction  following  forest  fires  or  logging 
operations. 

Some  seed  while  dormant  will  withstand  severe  conditions,  as  shown 
by  chemical  tests. 

Coniferous  seeds  are  known  to  be  viable  after  two  to  eight  years  of 
storage  in  the  forest  floor. 


STUDIES  IN  ENGINEERING 

1.  GEORGE  ALFRED  MANEY,  Secondary  Stresses  and  Other  Problems  in  Rigid 
Frames:  A  New  Method  of  Solution.     1915.     $0.25. 

2.  CHARLES  FRANKLIN  SHOOP,  An  Investigation  of  the  Concrete  Road-Making 
Properties  of  Minnesota  Stone  and  Gravel.     1915.     $0.25. 

3.  FRANKLIN  R.  MCMILLAN,  Shrinkage  and  Time  Effects  in  Reinforced  Con- 
crete.    1915.     $0.25. 

STUDIES  IN  THE  BIOLOGICAL  SCIENCES 

1.  HERBERT  G.  LAMPSON,  A  Study  on  the  Spread  of  Tuberculosis  in  Families. 
1913.     $0.50. 

2.  JULIUS  V.  HOFMANN,  The  Importance  of  Seed  Characteristics  in  the  Natural 
Reproduction  of  Coniferous  Forests.     1918.     $0.25. 

STUDIES  IN  LANGUAGE  AND  LITERATURE 

1.  ESTHER  L.  SWENSON,  An  Inquiry  into  the  Composition  and  Structure  of 
Ludus  Coventrize;  HARDIN  CRAIG,  Note  on  the  Home  of  Ludus  Coventriae.     1914. 

2.  ELMER  EDGAR  STOLL,  Othello:  An  Historical  and  Comparative  Study.     1915. 

3.  COLBERT  SEARLES,  Les  Sentiments  de  V Academic  Frangaise  sur  le  Cid:  Edition 
of  the  Text,  with  an  Introduction.     1916.     $1.00. 

4.  PAUL  EDWARD  KRETZMANN,  The  Liturgical  Element  in  the  Earlie 
of  the  Medieval  Drama.     1916.     $1.00. 

5.  ARTHUR  JERROLD  TIEJE,  The  Theory  of  Characterization  in  Prose  I 
prior  to  1740.     1916.     $0.75. 

CURRENT  PROBLEMS 

1.  WILLIAM  ANDERSON,  The  Work  of  Public  Service  Commissions.    1913.    $0.15 

2.  BENJAMIN  F.  PITTENGER,  Rural  Teachers'  Training  Departments  in  Min- 
nesota High  Schools.     1914.     $0.15. 

3.  GERHARD  A.  GESELL,  Minnesota    Public    Utility  Rates.     ! 

4*.  L.  D.  H.  WELD,  Social  and  Economic  Survey  of  a  Community  in  the  E 
River  Valley.     1915.     $0.25. 

5.  GUSTAV   P.   WARBER,   Social   and   Economic   Survey  of  a   C 
Northeastern  Minnesota.     1915.     $0.25. 

6.  JOSEPH  B.  PIKE,  Bulletin  for  Teachers  of  Latin.     ! 

7.'  AUGUST  C.   KREY,   Bulletin  for  Teachers  of  History.     : 

8.  CARL  SCHLENKER,  Bulletin  for  Teachers  of  German.     : 

9.  WILLIAM  WATTS  FOLWELL,  Economic  Addresses.     In  press. 


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